In a typical radio communications network, communication devices, also known as Mobile Stations (MSs) and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more Core Networks (CN). The radio access network covers a geographical area which is divided into coverage areas, such as cell areas, with each coverage area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. One base station may have one or more cells. A cell may be downlink and/or uplink cell. The base stations communicate over an air interface operating on radio frequencies with the user equipments within range of the base stations.
A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM).
General Packet Radio Service (GPRS) is a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications (GSM).
Enhanced Data rates for GSM Evolution (EDGE) also known as Enhanced GPRS (EGPRS), or International Mobile Telecommunications Single Carrier (IMT-SC), or Enhanced Data rates for Global Evolution is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM.
The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments.
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
The project covers cellular telecommunications network technologies, including radio access, the core transport network, and service capabilities—including work on codecs, security, quality of service—and thus provides complete system specifications. The specifications also provide hooks for non-radio access to the core network, and for interworking with Wi-Fi networks.
In some versions of the RAN as e.g. in UMTS and GSM, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs or BSCs are typically connected to one or more core networks.
Specifications for Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and are further evolved in coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the LTE radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein radio base station nodes are directly connected to the EPC network, i.e. a radio network controller concept as realized in UMTS with a Radio Network Controller (RNC) does not exist. In general, in EPS the functions of an RNC are distributed between eNBs and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio base stations without being controlled by RNCs.
Machine Type Communications (MTC) is an area within telecommunications, sometimes also referred to as M2M or Internet of Things (IoT), in which it is envisioned that all types of devices which may potentially benefit from communicating will do so. That is, everything from agriculture and/or industrial sensors and actuators to things in the smart home or workout gauges in the personal networks will be connected wirelessly.
MTC has in recent years shown to be a growing market segment for cellular technologies, especially for GSM and Enhanced Data Rates for GSM Evolution (EDGE) with its global coverage, ubiquitous connectivity and price competitive devices.
With more and more diverse MTC applications, more and more diverse set of MTC requirements arise. Among these there is a low-end market segment characterized by some or all of the following requirements compared with the current GSM technology:                Extended coverage        Long battery life        Low device complexity        Large number of connected devices        
Today's cellular systems are not always suitable for new applications and devices that follow with MTC and Internet of Things (IoT). For example, there is an objective to increase the coverage compared to existing services. In telecommunications, the coverage of a base station, is the geographic area where the base station is able to communicate with wireless devices. Some MTC networks are envisioned to be deployed in extreme coverage circumstances, such as basements of buildings or beneath the ground where radio signals suffer from severe attenuation.
At the 3GPP meeting GERAN#67 a new work item called ‘New Work Item on Extended Coverage (EC) GSM (EC-GSM) for support of Cellular Internet of Things’ was approved with the intention to improve coverage with 20 dB, to improve battery life time and to decrease device complexity. Later the name EC-GSM was changed to Extended-Coverage Global System for Mobile communications Internet of Things (EC-GSM-IoT), and these two names will be used interchangeably hereafter.
Cellular Internet of Things' provides IoT by means of a cellular system, such as EC-GSM-IoT.
An extended coverage, e.g. a coverage range beyond that of legacy GPRS/EGPRS operation may be achieved by blind physical layer repetitions in both uplink and downlink. The number of repetitions may be associated to a given Coverage Class (CC).
On a control channel, i.e. on an EC control channel, the coverage may be improved using blind physical layer repetitions of radio blocks while on a data channel, i.e. on an EC data channel, the coverage may be improved using a combination of blind physical layer repetitions and HARQ retransmissions of radio blocks. “Blind Physical Layer Repetitions” means that a predetermined number of repetitions are sent blindly, i.e. without feedback from the receiving end.
Logical channels supporting operation in extended coverage are referred to as Extended Coverage channels (EC-channels).
Taking the example of EC-GSM-IoT four different Coverage Classes are defined denoted as CC1, CC2, CC3 and CC4 respectively. Each Coverage Class is approximated with a level of extended coverage range compared to legacy GPRS/EGPRS operation. I.e. each Coverage Class represents a certain amount of degradation of a signal over noise ratio compared to legacy GPRS/EGPRS operation, e.g. 3 dB, such that the number of blind physical layer repetitions associated with each Coverage Class is proportional to its corresponding degradation compared to legacy GPRS/EGPRS operation. For example, for the EC Packet Data Traffic CHannel (EC-PDTCH) CC1 corresponds to one single transmission, CC2 corresponds to 4 transmissions, whereof 3 repetitions, also referred to as retransmissions, CC3 corresponds to 8 transmissions, whereof 7 repetitions, and CC4 corresponds to 16 transmissions, whereof 15 repetitions. Thus, CC1 corresponds to the coverage range of legacy GPRS/EGPRS operation, i.e. extended coverage not used.
Further, in EC-GSM-IoT a fixed predefined number of blind physical layer repetitions are applied per logical channel and per Coverage Class. The number of blind physical layer repetitions may differ between logical channels for the same Coverage Class.
The approach of blind physical layer repetitions on the EC-channels will result in a decrease in the data rates and thus longer latencies compared to the legacy GPRS/EGPRS operation for sending and receiving messages between the network, such as the core network, and the mobile stations. Non Access Stratum (NAS) messages are messages that are sent transparently via the radio access network between the mobile station and the core network, e.g. a Serving GPRS Support Node (SGSN). The NAS messages are supervised by timers defined in 3GPP TS 24.008 v13.3.0 Technical Specification Group Core Network and Terminals; Mobile radio interface Layer 3 specification; Core network protocols; Stage 3.
An independent solution for improving battery life time is extended DRX (eDRX) which allows a communication device to go into a sleep mode between paging occasions.
When a communications network tries to send data traffic to a communication device, the communications network uses a paging procedure, where a paging message, also referred to as a paging request message or page, is sent from a core network through a base station to the communication device. The paging message lets the RAN, e.g. the base station, and the communication device know that the core network is looking for the communication device. The communication device is expected to listen to a paging channel at certain time instants in order to receive the paging message. The paging message sent from the core network to the RAN does not necessarily comprise the same information as the paging message sent from the RAN to the communication device. On a Gb interface, i.e. between the SGSN and a Base Station System (BSS) the term PAGING-PS PDU is used. On the radio interface there are presently 4 messages used for paging: EC PAGING REQUEST message for EC, PAGING REQUEST TYPE 1, PAGING REQUEST TYPE 2, PAGING REQUEST TYPE 3. The choice of messages depends on type of device how many communication devices that are paged and with which identity (IMSI or P-TMSI).
In the interest of simplicity it is assumed that all communication devices supporting extended coverage GSM will also support eDRX. However, eDRX may still be supported by the communication device when it does not support extended coverage GSM.
From a network perspective, when eDRX is supported it may be deployed in all cells within a Routing Area while EC-GSM-IoT may be deployed on a cell level basis. In other words within a BSS coverage area, such as a Routing Area, there may be cells supporting eDRX but not EC-GSM-IoT.
EC-GSM-IoT may be introduced as a software update on legacy GPRS/EPGRS terminals. This means that initially there will be communication devices supporting both legacy GPRS/EGPRS mode as well as EC-GSM-IoT mode. As such, depending on device capability there will be limitations regarding which mode that may be used in a cell that supports only one or both of these modes.
A communication device and/or a cell that only supports EC-GSM-IoT mode is one that only supports the use of paging on the Extended Coverage Paging Channel (EC-PCH), an optimized RLC protocol, i.e. specific to the EC-GSM-IoT feature, and relaxed mobility management procedures on the assigned radio resources.
Similarly, a communication device and/or a cell that only supports legacy GPRS/EGPRS mode is one that only supports the use of the paging on the PCH, i.e. not on the EC-PCH, the legacy RLC protocol and legacy mobility management procedures on the assigned radio resources.
In order to reach a communication device supporting EC-GSM-IoT the BSS may send a page, such as an EC PAGING REQUEST message, to communication devices in an appropriate paging group. The page may be based on an appropriate coverage class. The SGSN may provide the coverage class in a page request, such as a PAGING-PS PDU, which it sends to the radio access network node 111. This means that the radio access network node 111 may take into account both eDRX and coverage class information provided in the PAGING-PS PDU to determine the specific set of EC-PCH radio resources to use when sending a corresponding page on the radio interface.
The SGSN may be provided with the current coverage class information for any given communication device whenever the BSS sends an UL-UNITDATA PDU comprising an uplink LLC PDU sent by that communication device. The SGSN may then include relevant cell ID and coverage class information in the PAGING-PS PDU(s).
In order to reach a communication device supporting EC-GSM-IoT the BSS may send the page using the appropriate coverage class.
EC-GSM-IoT communication devices, when located in a cell that supports EC-GSM-IoT, will search for paging messages on the EC-PCH channel which is mapped on a time slot (TS1) which is different from the legacy paging channel (TS0).
A communication device supporting eDRX and EC-GSM-IoT may wake up in a cell that doesn't support EC-GSM-IoT which means that the only relevant paging channel is the legacy paging channel on time slot 0 (2,4,6). I.e. legacy paging channels make use of time slot 0 at minimum but system information may indicate that one or more of time slots 2, 4 or 6 may also be used as paging channels.
This in turn implies that in order to reach the communication device the page is to be sent on the legacy paging channel.
The decision to send out a page request is made by a core network node, such as the SGSN. The paging strategy in the SGSN is implementation dependent, e.g. when the SGSN knows that the communication device is located in a small subset of cells the page request may only be sent to that particular subset of cells. Similarly, when the location of the communication device is unknown the SGSN may e.g. decide to send out the page in the entire routing area.
If the SGSN knows that the device is located in one specific cell then paging is not necessary, which for example is the case when the Ready Timer is running.
In some scenarios the SGSN provides an indication of more than one cell in the page request, such as a PAGING-PS PDU to the BSS along with Coverage Class information and an indication of an eDRX cycle.
If GPRS/EGPRS and/or eDRX is supported in a given cell, which is part of the Routing Area or the BSS area that the Paging-PS PDU message is directed to, but EC-GSM-IoT is not supported in the given cell the BSS does not know which paging channel the device is listening on and therefore it does not know if it is reachable in that given cell.
In other words, the communication device may be located in the given cell and may be listening to the legacy paging channel (TS0), or it may not be reachable in that cell.
The BSS then has no choice but to either send the page on the legacy paging channels of that cell simply hoping that the communication device is reachable therein or not send a page in that cell realizing that the communication device could in practice actually be reachable therein.
In the latter scenario the paging success rate will decrease if the communication device also supports legacy GPRS/EGPRS operation while in the former scenario the BSS may waste valuable paging resources if the communication device does not support legacy GPRS/EGPRS operation.